Explanation:
Let's solve the problem step by step.

**Let:**
- \( A \) = Average after the 11th innings
- \( T \) = Total runs after the 11th innings = \( 11A \)

**After the 12th innings:**
- The batsman scores 80 runs.
- New total runs = \( T + 80 = 11A + 80 \)
- New average = \( A + 3 \)

**Setting up the equation for the new average:**
\[
\frac{11A + 80}{12} = A + 3
\]

**Multiply both sides by 12 to eliminate the denominator:**
\[
11A + 80 = 12(A + 3)
\]
\[
11A + 80 = 12A + 36
\]

**Rearrange to solve for \( A \):**
\[
80 - 36 = 12A - 11A
\]
\[
44 = A
\]

**Now, find the new average after the 12th innings:**
\[
\text{New average} = A + 3 = 44 + 3 = 47
\]

**Final Answer:**
\[
\boxed{47}
\]